(a) Field of the Invention
This invention generally relates to a fan system for harnessing wind power. More particularly, but not by way of limitation, to a system that uses several fans of progressively larger fan diameter that are positioned in series.
(b) Discussion of Known Art
Wind power has long been recognized as a source of reliable, environmentally safe source of power. Accordingly, many devices for harnessing wind power have been developed. One example of these devices is shown in U.S. Pat. No. 1,142,502 to Donnelly. Donnelly teaches the use of a pair of different sized fans connected in series to one another. The type of fan and arrangement taught by Donnelly was popular in its day, but this design gave way to the use of long blades with airfoil sections. These blades are mounted to a gearbox that is used for transmitting rotational power harnessed through the blades to a generator.
Typically, wind turbines are supported at a considerable height above ground level. The reason for the elevated support is two-fold. First, the blades of the fan are typically very long, in the order of at least fifteen feet per blade. The length of the blade is dictated by the large amount of torque needed to turn the generator connected to the blade. Second, in order to obtain the full use of the blades, the fan must be position at a sufficiently high position above ground to position the blades in the wind stream that is relatively unaffected by the ground.
The placement of the blades at a high location above ground requires the use of a tall tower, which must be capable of resisting very large bending moments created by the wind forces on the fan at the top of the tower. These bending moments have made the creation of lightweight towers a problem that is seemingly impossible to solve. Thus wind power generation stations have been confined to being large permanent installations that include towers made from reinforced concrete or heavy gage steel construction.
The weight associated with the towers has made portable wind power generation stations unfeasible. Portable wind power generation stations are highly desirable due to the fact that the direction of prevailing wind in an area is not constant. Thus, a wind power generation system, or fan farm, may provide optimal performance during certain months of the year, and provide inefficient results during other times of the year. This variation in efficiency is due to the fact that, while the blades and generator assembly may rotate in order to align the assembly with the wind, the fixed position of the various fan installations causes some installations to remain in a wind shadow behind other fan installations.
Thus, in order to provide efficiency to the installations on a fan farm, it would be advantageous to be able to provide a wind power generation system or fan system that is portable, so that the alignment and arrangement of the individual fan stations may be rearranged in the field to allow the placement of these stations to be optimized.
Still further, there remains a need for a wind power generation system that reduces the bending moment created on the support structure, while still harnessing the torque required to rotate the generator. Thus, there remains a need for a wind power generation system that allows the support of the fan blades with a light-weight, efficient structure.
There remains a need for a wind power generation system that can use small amounts of wind to rotate large fans.